This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-303582 filed on Oct. 3, 2000.
The present invention relates to a vehicular power generator control apparatus for controlling a power generating state of a power generator by detecting a rotation speed of the power generator.
A vehicular power generator (a.c. generator) is used to charge a battery in running a vehicle and supplies power of ignition of an engine, illumination and other various electric equipment. A power generator control apparatus is connected to the power generator in order to regulate the output voltage of the power generator to be substantially constant even when its load state is changed. Particularly, in recent times, with an increase in electric loads, drive torque of the power generator tends to increase. When the drive torque of the power generator becomes excessively large in idling to rotate the engine, rotation of the engine becomes unstable. Therefore, the power generator control circuit is required to avoid such a situation by controlling the power generating state of the power generator.
For example, it is proposed in JP-A-6-284598 to restrain supply of field current until exceeding a predetermined rotation speed. By detecting a rotation speed of the power generator by monitoring one phase voltage (P-terminal voltage) of a stator coil, the supply of field current is limited. It is also proposed in JP-A-6-284597 to restrict the supply of field current when an engine is rotated at low speeds.
However, when leakage current is generated at inside of the power generator by being exposed to salt water and the leakage current flows to a P-terminal connected with one end of any phase of stator coils, voltage appearing at the P-terminal rises by being biased by an amount of voltage drop determined by the leakage current and input impedance of the P-terminal. Thereafter, although an alternating current component appears in voltage at the end portion of other phases of the stator coil, the P-terminal voltage is fixed to predetermined bias voltage determined by the leakage current. This state continues until voltages of the stator coils of respective phases other than that of the P-terminal becomes equal to or higher than a terminal voltage of a vehicle-mounted battery or equal to or lower than ground voltage and output current is taken out via a rectifying circuit. Therefore, when the leakage current is generated at the inside of the power generator, the power generation start rotation speed is extremely increased in comparison with its design value and accurate power generation control cannot be carried out.
The invention addresses the above drawbacks and has an object to provide a vehicular power generator control apparatus capable of firmly carrying out power generation control even when leakage current is generated at inside of the power generator.
A vehicular power generator control apparatus according to the present invention is provided with a voltage control circuit, a rotation speed detecting circuit, a leakage detecting circuit and a maximum conduction rate restricting circuit. The voltage control circuit controls output voltage of a power generator by interrupting switching devices connected in series with a field coil of the power generator. The rotation speed detecting circuit is connected to one phase terminal of stator coils of the power generator and detects a rotation speed of the power generator based on voltage appearing at the one phase terminal. The leakage detecting circuit detects that leakage current flows to the one phase terminal. The maximum conduction rate restricting circuit sets a maximum conduction rate prescribing an upper limit value of a conduction rate of switching device to a first rate until the rotation speed of the power generator detected by the rotation speed detecting circuit exceeds a predetermined value and sets the maximum conduction rate to a second rate higher than the first rate when the leakage current is detected by the leakage detecting circuit.
When generation of the leakage current is detected, regardless of the rotation speed of the power generator, by changing the maximum conduction rate from the first rate to the second rate higher than the first rate, current flowing in a field coil is increased, voltage induced in the stator coil is made to rise, output current is taken out via a rectifying circuit. Thus, the leakage current which flows to the one phase terminal can be reduced, and therefore the rotation speed of the power generator can accurately be detected and power generation control can firmly be carried out.
It is preferable that the leakage detecting circuit detects generation of the leakage current when a state in which the voltage appearing at the one phase terminal exceeds a voltage of a predetermined detection threshold used in detecting the rotation speed of the rotation speed detecting circuit, continues for a predetermined time period. The detecting operation by the rotation speed detecting circuit cannot be carried out by applying predetermined bias voltage by the leakage current flowing to the one phase terminal, and therefore the state is determined to indicate as generation of the leakage current. The maximum conduction rate is changed, and thereby the power generator is restored to a state capable of firmly detecting the rotation speed of the power generator.
It is also preferable that a start instruction detecting terminal is provided for receiving a start instruction signal transmitted from an outside apparatus. When the start instruction signal is not inputted to the start instruction detecting terminal, even when the leakage current is detected by the leakage detecting circuit, the maximum conduction rate control circuit stops an operation of setting the maximum conduction rate to the second rate. When the operation start instruction signal is not inputted and power stops generating, in the case in which the leakage current is generated at inside of the power generator for some reason and generation of the leakage current is detected by the leakage detecting circuit, the field current can be prevented from increasing and discharge of the battery can be restrained by stopping to control to change the maximum conduction rate from the first rate to the second rate for increasing field current.